Photoplethysmography with controlled application of sensor pressure

Abstract

Systems, methods, and devices for obtaining consistently reproducible diagnostic measurements with a photoplethysmographic sensor are provided. In one embodiment, a method for obtaining such a diagnostic measurement includes applying a pressure between a photoplethysmographic sensor and a patient, increasing the pressure until the photoplethysmographic sensor outputs a plethysmographic waveform of minimal amplitude, decreasing the pressure by a predetermined fraction, and obtaining a diagnostic measurement using the photoplethysmographic sensor. The pressure may be applied using a pressure device that includes, for example, a clip, a wrap, an inflatable balloon or bladder, or an inflatable cuff, or any combination thereof.

What is claimed is: 
     
       1. A patient monitor comprising:
 circuitry configured to:
 receive a plethysmographic signal from a sensor when the sensor is applied to a patient; 
 control a pressure device to increase an applied pressure between the sensor and the patient until identifying a maximal pressure that occurs when the sensor outputs the plethysmographic signal of minimal amplitude; and 
 decrease the pressure by a predetermined fraction of the maximal pressure to enable a diagnostic measurement using the sensor. 
 
 
     
     
       2. The patient monitor of  claim 1 , wherein the circuitry is configured to determine the diagnostic measurement based on the plethysmographic signal after decreasing the pressure by the predetermined fraction. 
     
     
       3. The patient monitor of  claim 2 , wherein the diagnostic measurement comprises a pulse oximetry measurement or a measurement of total hemoglobin, or a combination thereof. 
     
     
       4. The patient monitor of  claim 1 , wherein the patient monitor is connected to a network via a network interface. 
     
     
       5. The patient monitor of  claim 4 , wherein the patient monitor is wirelessly connected to the network. 
     
     
       6. The patient monitor of  claim 1 , wherein the predetermined fraction is approximately one half. 
     
     
       7. The patient monitor of  claim 1 , wherein the circuitry is configured to control the pressure device to decrease the pressure to between approximately 50 and 70 mm Hg when the maximal pressure is between approximately 100 and 150 mm Hg when the patient has a blood pressure in a normal range. 
     
     
       8. The patient monitor of  claim 1 , wherein the circuitry is configured to increase or to decrease the pressure applied by the pressure device via an electronic signal. 
     
     
       9. The patient monitor of  claim 1 , wherein the circuitry is configured to increase or to decrease the pressure applied by the pressure device via a signal of supplied liquid or gas. 
     
     
       10. The patient monitor of  claim 1 , comprising a pressure sensor decoder configured to receive an indication of the applied pressure via a pressure sensor and to provide the circuitry with data related to the applied pressure. 
     
     
       11. The patient monitor of  claim 1 , wherein the circuitry is configured to access routines stored in a memory of the patient monitor and to execute the routines to control the pressure device. 
     
     
       12. A system comprising:
 a sensor configured to generate a plethysmographic signal when applied to a tissue site of a patient; and 
 a patient monitor configured to receive the plethysmographic signal and to control a pressure applied to the tissue site, wherein the patient monitor is configured to increase the pressure applied until identifying a maximal pressure that occurs when the plethysmographic signal reaches a minimal amplitude, and to decrease the pressure applied by a predetermined fraction of the maximal pressure to enable a diagnostic measurement using the sensor. 
 
     
     
       13. The system of  claim 12 , comprising a pressure device coupled to the sensor, wherein the patient monitor is configured to control the pressure device to increase or to decrease the pressure applied to the tissue site. 
     
     
       14. The system of  claim 13 , wherein the pressure device comprises a clip, a wrap, an inflatable balloon or bladder, or an inflatable cuff, or any combination thereof. 
     
     
       15. The system of  claim 12 , comprising a pressure sensor configured to provide data related to the applied pressure to the patient monitor. 
     
     
       16. The system or  claim 15 , wherein the pressure sensor is coupled to the sensor. 
     
     
       17. The system of  claim 12 , wherein the patient monitor is configured to determine a pulse oximetry measurement or a measurement of total hemoglobin, or a combination thereof, based on the plethysmographic signal. 
     
     
       18. A patient monitor comprising:
 circuitry configured to:
 receive a plethysmographic signal from a plethysmographic sensor when the plethysmographic sensor is applied to a patient tissue site; 
 receive data indicative of a first thickness of a plethysmographic sensor while attached around a patient tissue site at a minimal pressure sufficient to establish contact between the patient and the sensor; 
 compress the plethysmographic sensor attached around the patient tissue site until a maximal pressure is reached, wherein the maximal pressure is a lowest pressure that causes the plethysmographic sensor to output the plethysmographic signal of minimal amplitude; 
 receive data indicative of a second thickness of the plethysmographic sensor while attached around the patient tissue site at the maximal pressure; and 
 decompress the plethysmographic sensor attached around the patient tissue site until the plethysmographic sensor has an intermediate thickness between the first thickness and the second thickness, wherein the intermediate thickness is a predetermined fractional distance between the first and the second thickness. 
 
 
     
     
       19. The patient monitor of  claim 18 , wherein the circuitry is configured to determine a diagnostic measurement of interest using the plethysmographic sensor after the plethysmographic sensor is decompressed to the intermediate thickness. 
     
     
       20. The patient monitor of  claim 19 , wherein the diagnostic measurement of interest is a pulse oximetry measurement or a measurement of total hemoglobin, or a combination thereof.